Currently, a standard zoom optical system for a movie camera has the capability of focusing on objects located at any distance between about five feet and infinity. The focusing function in this range is normally performed by a set of lenses referred to as the focusing group, located at the front end of the optical system.
The desired framing of the scene may be adjusted by adjusting the "zoom" of the lens. This is accomplished by moving a variator lens group and a compensator lens group, which are mutually displaceable in a predetermined relationship. A common zoom range in a zoom optical system for a movie camera is 7-45 millimeters.
It is desirable that the zoom lens be capable of focusing on objects located closer than five feet. There are and have been zoom lenses on the market and patented which can focus on objects in the extreme closeup or "macro" range. These currently available lenses have means selectively to be placed in the normal zoom mode or in a macro mode. In the former mode, the zoom lens can be focused on objects say beyond five feet, while in the macro mode the lens may be focused on objects closer than five feet.
However, all such currently available lenses as far as known by the applicant herein, do not offer what may be characterized as a variable focal length or a variable magnification within the macro range. In other words, an object located at for example three feet may be focused by these lenses, but the reduction ratio is fixed; i.e., the size of the scene for an object located in the macro range is fixed. The reason for this is because currently available zoom lenses have macro capability only at one end of the normal zoom range. Some such lenses have macro capability in the range beyond the wide angle end of the zoom range and others have macro capability in the range beyond the telephoto end of the zoom range.
So as to increase the versatility of a zoom lens and provide for a more selectable framing or reduction in extreme closeup photography, two macro modes have been mentioned in at least one prior U.S. patent, although no such zoom lens having dual macro capability is known to be or have been on the market.
Reference may be had to U.S. Pat. No. 3,884,555, to Suwa et al. which discloses some possible forms in which macro capability exists at both ends of the zoom range. For example, in FIG. 1, such a system is disclosed. The common method of construction is to use camming slots in the sleeves that carry the variator and compensator lens groups. A linear camming slot, that is one whose axis is substantially planar, is much easier to manufacture within the exceedingly close tolerance which is required of lens systems. Thus, the nonlinear movement of the compensator and variator lenses, particularly in the macro ranges as shown in FIGS. 1 and 2 of the Suwa et al. patent, makes it uneconomical to manufacture.
There is currently in the marketplace a zoom lens of the type described herein with a normal range and a macro capability at the wide angle end of the zoom range. This particular system is sold by Bell & Howell Company, the assignee of the present application, but it has no macro capability beyond the telephoto end of the normal zoom range.